The present invention generally relates to the field of retinal imaging. Retinal imaging, as used in this application, refers to illuminating the human retina with non harmful visible or near infra-red (NIR) light, viewing the retina, and (optionally) capturing one or more images. The simplest retinal imaging device is the indirect ophthalmoscope. This device includes a low power white (broadband visible) light source and an optical system that includes an ocular. The instrument is placed between the patient's eye and the practitioner's eye, the patient's retina is illuminated, and the image of the patient's retina is transferred to the practitioner's retina. This type of screening examination is typically performed by primary care physicians. Indirect ophthalmoscopes have limited diagnostic capabilities, and do not have means for recording images, so if the screening exam indicates pathology, the patient is generally referred to an eye specialist (ophthalmologist or optometrist) for an examination with a more sophistical retinal imaging device that incorporates an electronic imaging device such as a CCD or CMOS camera, along with an image recording and archiving system. These retinal imaging devices are known as either “retinal cameras” or “fundus cameras”. “Fundus” refers to the back of the eye. Typically retinal cameras and fundus cameras are large (table-top sized) and expensive and are used almost exclusively by eye specialists.
Retinal exams are used to visually screen for retinal abnormalities and to monitor the progression of known pathologies. Pathologies of the retina include malignancies, retinal detachment, age-related macular degeneration, retinitis pigmentosa, retinal infections, and diabetic retinopathy. Diabetic retinopathy is the leading cause of blindness in the world and with the rapid increase in the incidence and prevalence of diabetes, blindness from diabetes is a rapidly growing problem. If diagnosed early enough and treated appropriately (drugs are quite effective), blindness is generally preventable. Unfortunately, in the U.S. many people do not have access to eye specialists. This may result from poor compliance, lack of transportation to distantly-located eye specialists, or from reduced mobility due to obesity or other diabetic pathologies. The problem is more severe in many other parts of the world where health services are even less accessible than they are in the U.S. There is therefore great interest by health services organizations and governments around the world in means to increase access to diagnostic retinal imaging services.